drm/hisilicon: Ensure LDI regs are properly configured.

This patch fixes the following soft lockup:
  BUG: soft lockup - CPU#0 stuck for 23s! [weston:307]

On weston idle-timeout the IP is powered down and reset
asserted. On weston resume we get a massive vblank
IRQ storm due to the LDI registers having lost some state.

This state loss is caused by ade_crtc_atomic_begin() not
calling ade_ldi_set_mode(). With this patch applied
resuming from Weston idle-timeout works well.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Cc: stable@vger.kernel.org
Reviewed-by: Xinliang Liu <xinliang.liu@linaro.org>
Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>